Cannot find passwd file?

When trying to change the password of a user on my system, with
"passwd <user>", I get the error "Cannot open the password file."
I have no idea how this happened, but I am logged in as root,
and /etc/passwd is mod 644... I have shadow passwords installed,
and /etc/shadow is mod 640.
I can cat < /etc/shadow and cat < /etc/passwd just fine.
The pwck command gives an error of "cannot open file /etc/passwd".
Ideas, anyone?
Colin McMillen
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